Carbon sequestration is a viable alternative to reduce the emissions of the greenhouse gas carbon dioxide (CO2) from large point sources. It holds the potential to provide deep reductions in greenhouse gas emissions. Carbon sequestration is a two-step process where the capture of carbon dioxide from a gas stream is followed by permanent storage. The capture step for carbon dioxide represents a major cost in the overall process.
Of particular interest are power generation point sources that use fossil fuels. Since nearly one-third of the anthropogenic CO2 emissions are produced by these facilities, conventional coal-burning power plants and advanced power generation plants—such as integrated gasification combined cycle—present opportunities where carbon can be removed and then permanently stored. At the current time, pulverized coal-fired-base steam cycles have been the predominant electric power generation technology. These will continue to be used predominantly in the near future. Technologies for capturing CO2 will need to be applied to new more efficient coal-fired facilities and will need to be retrofitted onto existing plants.
For coal-fired power plants, the conventional scrubbing system that is currently the comparative baseline for all other capture technologies is monoethanolamine (MEA) scrubbing. This wet scrubbing process removes the CO2 in an absorber and then regenerates the spent scrubbing liquor in a vessel by indirectly heating the solution with plant steam. Although there have been large scale commercial demonstrations of this technology, the process has several disadvantages, such as a high heat of reaction, low working capacity, corrosiveness of the solution, the susceptibility of being poisoned, and most notably, its need to be in an aqueous solution. This latter disadvantage results in a large energy need to regenerate the spent solution, especially the sensible heating of the water, which is a minimum of 70-wt % of the solution. The water is recognized as an inert carrier between the absorption and regeneration steps. Another energy loss while regenerating the spent MEA solution includes evaporative heat loss of vaporizing liquid water.
One type of novel CO2 capture technology that can be applied to various gas streams has, as a basis, dry regenerable solid sorbents. Examples of these types of sorbents are zeolites, activated carbon, alkali/alkaline earth metals, immobilized amines, metal organic framework, etc. A specific sorbent class that shows significant advancement are amine-based solid sorbents, such as Basic Immobilized Amine Sorbents (BIAS). These sorbents consist of amines (primary, secondary, tertiary, or a combination thereof) deposited onto a porous substrate. The manner of deposition is important and can be random or structured deposition of the amine onto the support (silica, polymer, etc.) The sorbent process may act in a similar fashion to the wet scrubbing in that the sorbent would be transported between the absorption step and the regeneration step and in that the sorbent is regenerated by a temperature-swing application.
One of the main benefits in using the solid sorbent is the elimination of the sensible heat for the liquid water as compared to MEA. A secondary benefit lies in the lower heat capacity for the solid versus the liquid solvent, also serving to lower the sensible heat required. More CO2 can be absorbed on a weight or volume basis with the amine-based solid sorbents, so the sorbent system is capable of a significant decrease in the heat duty for the regeneration step. A lower cost of energy service as compared to amine wet scrubbing may also result. Thus amine-based solid sorbents have the capability to improve the overall energetics of CO2 capture.
Effective amine-based solid sorbent methodologies are needed for carbon dioxide capture, whether the capture occurs in combustion or gasification power generation systems, or in other applications, such as natural gas cleanup. Because of the high concentration of carbon dioxide in any of these feed streams, a large quantity of the gas will be reacting with the sorbent and thus produce considerable amounts of exothermic heat. This heat must be removed from the sorbent to prevent temperature instability within the reactor, to assure the sorbent will operate at optimum temperature, and to eliminate the potential degradation of the sorbent because of high temperature excursions. Reactor designs are available to eliminate heat problems. However, the presence of moisture in the various process gas streams can have a tremendous impact on the energetics of the system. Indirect/direct steam regeneration will have a significant advantage in the regeneration step with respect to CO2 regeneration, and adsorption/desorption as related to water within the process steps will potentially represent an energy loss unless controlled. It would be advantageous to provide a methodology whereby the CO2 absorption and water adsorption of amine-based solid sorbents were effectively compensated for, and regeneration energy losses mitigated.
Methodologies utilizing selected amine-based solid sorbents have discussed steam regeneration and subsequent air drying of the amine-based solid sorbent in a cyclic process. Typically the methodologies have relied on a stationary reactor where the sorbent does not floe between adsorption and regeneration steps. See e.g., U.S. patent application Ser. No. 12/741,600, filed by Chuang, based on PCT/US08/12570 filed Nov. 7, 2008. These methodologies discuss the use of dry air to evacuate steam following regeneration, however they do not address water loading manipulations based on inherent absorption and desorption behavior of the sorbent. Such an approach where subsequent water loading behaviors during the cyclic processes are ignored, and where a dry air flow is specified solely for the evacuation of surrounding steam, can lead to the significant transfer of adsorbed water from an absorber to a regenerator. Such transfer can produce significant regeneration losses and reduction in the CO2 capacity of a sorbent.
It would be advantageous to provide a method of adsorbing CO2 using an amine-based solid sorbent where regeneration losses and CO2 capacity reductions could be mitigated through proper adsorbed water management during the process, by considering the manner in which H2O and CO2 respectively are sorbed and desorbed during a cyclic process. Such a process would allow for vessels sized to achieve acceptable CO2 absorption and regeneration loads to be optimized through the water management. The process should provide for integration with existing power or fuel production facilities, and should be applicable to temperature and pressure ranges which avoid oxidative degradation of the amine-based solid sorbent while minimizing energy and infrastructure requirements.
Accordingly, it is an object of this disclosure to provide a method of adsorbing CO2 using an amine-based solid sorbent whereby regeneration losses and CO2 capacity reductions are mitigated through proper adsorbed water management during the cyclic process.
Further, it is an object of this disclosure to provide a method of adsorbing CO2 using an amine-based solid sorbent whereby the manner in which H2O and CO2 are sorbed and desorbed, so that vessels sized to achieve acceptable CO2 absorption and regeneration loads can be optimized through the water management.
Further, it is an object of this disclosure to provide a method of adsorbing CO2 using an amine-based solid sorbent whereby substantially equalized absorber and regenerator moisture loadings may result, so that the thermal energy in a steam regeneration process is applied maximally to CO2 desorption, without the necessity for desorbing H2O adsorbed in the CO2 absorption process.
Further, it is an object of this disclosure to provide a method of adsorbing CO2 using an amine-based solid sorbent where the method can be integrated with existing power or fuel production facilities, in order to provide a relatively pure CO2 stream for subsequent sequestration or utilization.
Further, it is an object of this disclosure to provide a method of adsorbing CO2 using an amine-based solid sorbent where the methodology can be applied to temperature and pressure ranges avoiding oxidative degeneration of the amine-based solid sorbent while minimizing energy and infrastructure impacts.
These and other objects, aspects, and advantages of the present disclosure will become better understood with reference to the accompanying description and claims.